diff --git a/src/main/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPlugin.java b/src/main/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPlugin.java
index 230d755..d6fbd1e 100644
--- a/src/main/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPlugin.java
+++ b/src/main/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPlugin.java
@@ -9,6 +9,7 @@
 import ch.interlis.iom.IomObject;
 import ch.interlis.iox_j.jts.Iox2jtsext;
 import ch.interlis.iox_j.validator.Value;
+import com.vividsolutions.jts.geom.Coordinate;
 import com.vividsolutions.jts.geom.Geometry;
 import com.vividsolutions.jts.geom.GeometryFactory;
 
@@ -70,7 +71,7 @@ private Value isInsideArea(String usageScope, Collection<IomObject> objects, Pat
                         Geometry::union
                 ));
 
-        List<Geometry> sortedGeometries;
+        List<Map.Entry<ValueKey, Geometry>> sortedGeometries;
         ValueKey firstKey = geometriesByCodeValue.keySet().iterator().next();
         Type keyType = firstKey.getType();
 
@@ -88,33 +89,48 @@ private Value isInsideArea(String usageScope, Collection<IomObject> objects, Pat
             return Value.createSkipEvaluation();
         }
 
+        boolean result = true;
         for (int i = 0; i < sortedGeometries.size() - 1; i++) {
-            Geometry current = sortedGeometries.get(i);
-            Geometry next = sortedGeometries.get(i + 1);
-
-            if (!next.contains(current)) {
-                return new Value(false);
+            Map.Entry<ValueKey, Geometry> current = sortedGeometries.get(i);
+            Map.Entry<ValueKey, Geometry> next = sortedGeometries.get(i + 1);
+
+            if (!next.getValue().contains(current.getValue())) {
+                Geometry offendingGeometry = current.getValue().difference(next.getValue());
+                Coordinate position = offendingGeometry.getCoordinate();
+                String offendingEnvelopeWkt = offendingGeometry.getEnvelope().toText();
+
+                String currentCode = current.getKey().getStringValue();
+                String nextCode = next.getKey().getStringValue();
+
+                logger.addEvent(logger.logErrorMsg(
+                        "IsInsideAreaByCode found an invalid overlap between code '{0}' and '{1}'. The offending geometry is inside this envelope: {2}",
+                        position.x,
+                        position.y,
+                        position.z,
+                        currentCode,
+                        nextCode,
+                        offendingEnvelopeWkt));
+
+                result = false;
             }
         }
 
-        return new Value(true);
+        return new Value(result);
     }
 
-    private List<Geometry> sortByEnumValues(Map<ValueKey, Geometry> map, EnumerationType enumType) {
+    private List<Map.Entry<ValueKey, Geometry>> sortByEnumValues(Map<ValueKey, Geometry> map, EnumerationType enumType) {
         List<String> enumValues = enumType.getValues();
 
         return map.entrySet()
                 .stream()
                 .sorted(Comparator.comparingInt(entry -> enumValues.indexOf(entry.getKey().getStringValue())))
-                .map(Map.Entry::getValue)
                 .collect(Collectors.toList());
     }
 
-    private List<Geometry> sortByNumericValues(Map<ValueKey, Geometry> map) {
+    private List<Map.Entry<ValueKey, Geometry>> sortByNumericValues(Map<ValueKey, Geometry> map) {
         return map.entrySet()
                 .stream()
                 .sorted(Comparator.comparingDouble(entry -> entry.getKey().getNumericValue()))
-                .map(Map.Entry::getValue)
                 .collect(Collectors.toList());
     }
 
diff --git a/src/test/data/IsInsideAreaByCode/SetConstraints.ili b/src/test/data/IsInsideAreaByCode/SetConstraints.ili
index ab39039..1c6fdd9 100644
--- a/src/test/data/IsInsideAreaByCode/SetConstraints.ili
+++ b/src/test/data/IsInsideAreaByCode/SetConstraints.ili
@@ -25,6 +25,7 @@ MODEL TestSuite
       codeNumeric : CodeNumeric;
       surface : SURFACE WITH (STRAIGHTS) VERTEX CHKoord WITHOUT OVERLAPS > 0.001;
 
+      !!@ ilivalid.msg = "Custom message."
       SET CONSTRAINT insideAreaConstraintEnum: NGK_SO_FunctionsExt.IsInsideAreaByCode(ALL, "surface", "codeEnum");
       SET CONSTRAINT insideAreaConstraintNumeric: NGK_SO_FunctionsExt.IsInsideAreaByCode(ALL, "surface", "codeNumeric");
     END BaseClass;
diff --git a/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/AssertionHelper.java b/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/AssertionHelper.java
index 00ff0dc..5c0a881 100644
--- a/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/AssertionHelper.java
+++ b/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/AssertionHelper.java
@@ -60,4 +60,19 @@ public static void assertLogEventsContainMessage(List<IoxLogEvent> logs, String
             fail(String.format("The logs are missing the message <%s>.", expectedMessageRegex));
         }
     }
+
+    /**
+     * Asserts that the logs contain the expected message regex a specific number of times.
+     *
+     * @param logs The logs to check.
+     * @param expectedMessageRegex The regex to match.
+     * @param expectedMatchCount The expected number of matches.
+     */
+    public static void assertLogEventsMessages(List<IoxLogEvent> logs, String expectedMessageRegex, long expectedMatchCount) {
+        Pattern pattern = Pattern.compile(expectedMessageRegex);
+        long actualMatchCount = logs.stream().filter(log -> pattern.matcher(log.getEventMsg()).find()).count();
+        if (actualMatchCount != expectedMatchCount) {
+            fail(String.format("Expected %d messages to match the regex <%s> but found %d.", expectedMatchCount, expectedMessageRegex, actualMatchCount));
+        }
+    }
 }
diff --git a/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPluginTest.java b/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPluginTest.java
index cba2dd8..6f34ea1 100644
--- a/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPluginTest.java
+++ b/src/test/java/ch/geowerkstatt/ilivalidator/extensions/functions/ngk/IsInsideAreaByCodeIoxPluginTest.java
@@ -29,8 +29,13 @@ public void setConstraintOk() throws Ili2cFailure, IoxException {
     @Test
     public void setConstraintFail() throws Ili2cFailure, IoxException {
         vh.runValidation(new String[]{TEST_DATA_FAIL}, new String[]{ILI_FILE});
-        Assert.equals(2, vh.getErrs().size());
-        AssertionHelper.assertConstraintErrors(vh, 1, "insideAreaConstraintEnum");
+        Assert.equals(9, vh.getErrs().size());
+
+        AssertionHelper.assertLogEventsMessages(vh.getErrs(), "^IsInsideAreaByCode found an invalid overlap between code 'code_2' and 'code_3'", 1);
+        AssertionHelper.assertLogEventsMessages(vh.getErrs(), "^IsInsideAreaByCode found an invalid overlap between code 'code_3' and 'code_4'", 1);
+        AssertionHelper.assertLogEventsMessages(vh.getErrs(), "^IsInsideAreaByCode found an invalid overlap between code '22' and '33'", 1);
+        AssertionHelper.assertLogEventsMessages(vh.getErrs(), "^IsInsideAreaByCode found an invalid overlap between code '33' and '44'", 1);
+        AssertionHelper.assertLogEventsMessages(vh.getErrs(), "^Custom message\\.$", 4);
         AssertionHelper.assertConstraintErrors(vh, 1, "insideAreaConstraintNumeric");
     }
 }